Time-delay network



July 4, 1950 M. J. D: TORO 2,513,921

' TIME DELAY NETWORK Phase Shift Phase Shift Frequency FIG. 3 INVENTOR. MICHAEL J. DiTORO ATTORN EY July 4, 1950 J, 0| TORO 2,513,921

TIME DELAY NETWORK Filed April 8, 1947 2 Sheets-Sheet 2 MICHAEL J. DiTORO ATTO R NEY iatentecl July 4, 1950 TIME-DELAY NETWORK Michael J. Di Toro, Brooklyn, N. Y., assignor t Hazeltine Research, Inc., Chicago, 111., a. corporation of Illinois Application April 8, 1947, Serial No. 740,208

'7 Claims.

This invention relates, in general, to time'- delay networks for translating signal pulses and for efiecting a relatively long time delay in networks of comparatively small physical size. The invention is especially suited for inclusion in networks adapted to translate signal pulses having a duration which may be less than the delay of the network and is related to copending application Serial No. 626,357, filed November 2, 1945, in the name of Michael J. Di Toro, now abandoned.

Time-delay networks, as such, have long been known in the art and have taken the form of a circuit unbalanced or balanced with respect to ground. While the invention may be utilized with either t pe, it may be fully understood from a consideration or" its application to an unbalanced arrangement. One prior construction of an unbalanced network comprises a single distributed winding insulated from but electrically coupled along its length to a conductive member, such as a longitudinally slotted conductive core structure positioned Within the winding. The capacitance between the winding and its core structure supplies the distributed capacitance of the network, which together with the inductance of the windin determines the total time delay. Input and output terminals are located at opposite ends of the winding so that signals applied to the input terminals are derived at the output terminals after some delay. Where long time delays are to be realized with networks of practical and useful physical dimensions, the distributed winding has a large number of turns per unit length and is frequently wound over a core structure of high permeability to increase the total series inductance.

Arrangements of the type described are satisfactory for many installations but are subject to a particular type of phase distortion which may be undesirable in other installations. This distortion is attributable to the substantial inductive coupling which exists between the closely spaced winding turns and tends to provide asymmetrical distortion of an applied symmetrical pulse. Such distortion is especially pronounced where the network includes a high-permeability core structure and when translating pulses having a duration less than the network delay.

Prior arrangements have been proposed in which the winding turns have such a large spacing that the inductive coupling between turns is minimized to avoid the distortion mentioned. Such structures are undesirable in that they have an unwieldy physical size when employed to obtain long time delays. It has also been proposed that a complex core structure be used with a winding having a relatively large spacing between turns. The core structure in that case is anisotropic, having a low permeability in the axial direction of the winding and as high a permeability as possible in the radial direction to confine the magnetic field of each turn in order to minimize the inductive coupling between turns. This construction is undesirable in view of the difiiculty encountered in fabricating a core which effectively minimizes the interturn inductive coupling through magnetic shielding of this type and also because of the large physical dimensions necessary to realize long time delays.

It is an object of the present invention, therefore, to provide an improved time-delay network adapted to translate signal pulses, the duration of which may be less than the delay of the network, and which avoids one or more of the abovementioned limitations of prior constructions.

It is another object of the invention to provide a new and improved time-delay network of simplified construction adapted to produce long time delays with a minimum amount of phase distortion, even though the pulse translated may have a duration less than the delay of the network.

It is a specific object of the invention to provide a new and improved phase compensating or correcting arrangement in a time-dela network of otherwise conventional construction so that pulses which may have a duration less than the delay of the network may be translated with substantially no phase distortion.

In accordance with the invention a time-delay network adapted to translate a signal pulse, the duration of which may be less than the delay of the network, comprises an elongated winding having a substantial inductive coupling between turns tending to cause asymmetrical distortion in one sense of an applied symmetrical pulse. One system of conductive surfaces is associated in coaxial relation with the winding, has a high resistivity to circulating currents, and is insulated from but electrically coupled to a major portion of the winding to provide a distributed shunt capacitance for the network. Another system of conductive surfaces, comprising a plurality of rings having a low resistivity to circulating cur rents and spaced along the winding, periodically varies the inductance thereof to simulate in the network a low-pass filter tending to cause asymmetrical distortion in a complementary sense of an applied pulse. The spacing and width of the rings are proportioned relative to the interturn inductive coupling of the winding so that an applied symmetrical pulse is translated through the network with a distortion which is substantially less than the larger of the asymmetrical distortions caused b the winding and the simulated low-pass filters.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the drawings, Fig. 1 is a schematic representation of a three-terminal time-delay network embodying the present invention; Figs. 2a, 2b, and 3 comprise curves utilized in explaining an operating characteristic of the network of Fig. 1; and Figs. 4, 5, and 6 individually represent a modified form of unbalanced network constructed in accordance with the invention.

Referring now more particularly to Fig. 1, the time-delay network there represented is of the unbalanced or three-terminal type for translating signal pulses included within a predetermined range of frequencies. This network is in the form of a simulated transmission line and comprises an elongated or distributed winding Iii. The winding has a large number of turns per unit length in order that a relatively long time delay may be realized with a network of small physical dimensions. This close spacing of the winding turns establishes a substantial inductive coupling between turns which tends to cause asymmetrical distortion in one sense of an applied symmetrical pulse.

The nework also comprises an elongated conductive core structure ll coaxially disposed within and insulated from winding ID, the insulation being supplied by a tape or sleeve l2 of dielectric material interposed between the winding and its core. The insulating member I2, of course, may be omitted where the insulation of winding H) has sufficiently high dielectric properties. 'In order to compensate the effects of the asymmetrical distortion attributable to the interturn inductive coupling, the core structure, presently to be described in detail, is arranged to provide systems of conductive surfaces which establish in alternate portions of the network substantially different values of series inductance to simulate in the network a low-pass filter.

The core structure ll may have any desired cross-sectional configuration but will be assumed to be circular in section. It may take the form of a tube of thermoplastic resin or glass having a conductive coating applied to its outer periphery to establish the resistivity to circulating currents to be mentioned hereinafter, or it may be similar to the customary slotted, conductive cylinder. The latter expedient has been represented in the drawing but the core, instead of having one or several slots each extending along substantiall its entire length, includes one or more series of aligned, identical relatively short slots l3a-'l3d, inclusive. In the usual construction, the slot lengths are long compared with their width and they may be considered to cause the conductive member ll efiectively to include one system of conductive surfaces designated by dimensions ilaelld, inclusive. Each component of this system of surfaces has a high resistivity to circulating currents because each such component is interrupted, having'a discontinuity at each associated one of the longitudinally extending series of slots ltd-I301. The separation of succeeding slots is small compared with the length of any slot so that the system of conductive surfaces Hal-l Id, under consideration, is electrically or capacitively coupled to a major portion of winding [0 to provide the requisite distributed shunt capacitance for the network.

It is apparent that the sections of conductive member ll intermediate its spaced longitudinal slots comprise a plurality of rings which may be thought of as constituting another system of conductive surfaces designated liaf-He, inclusive. Inasmuch as the ring sections are continuous, they present a low resistivity to circulating currents, that is, low in comparison with the resistivity of the sections l la-I Id. The rings, being spaced along the winding, periodically vary the inductance thereof to simulate in the network a low-pass filter for effecting phase compensation or correction.

An input terminal 15 is provided at one end of winding Ill and an output terminal it for deriving delayed signals from the nework is connected to the opposite end of the winding. The elongated conductive member H is connected to a third or common terminal ll which is usually a ground connection, as illustrated.

The described arrangement will be seen to constitute an unbalanced or three-terminal net work. It is said to be a three-terminal network since it has an input terminal 15, an output terminal I8 and a common terminal ii. The network has a given total time delay proportional to the geometric mean of its total effective series inductance and total effective shunt capacitance. The diameter and length of the core structure, the size and type of conductor utilized in fabricating winding Ill and the number and pitch of the winding convolutions are selected to afford such values of total series inductance and total shunt capacitance that the network produces a desired total time delay. In this connection, it will be appreciated that an increase in the diameter of the core structure and winding results in higher values of inductance and capacitance, while increasing the permeability of the core or the number of winding turns per unit length increases primarily the inductance.

In analyzing the phase characteristics of the I network, consideration must be given to the interturn inductive coupling of winding l0 and the eifect of the described conductive systems embodied in the single conductive member H. It may be shown that the interturn inductive coupling causes the effective inductance of the network to decrease with frequency. Where the core structure has a high permeability, this variation of effective inductance with frequency is exaggerated. The phase-shift constant of the network is proportional to the square root of its effective inductance and, therefore, also tends to vary with frequency because of the substantial interturn inductive coupling of winding iii. For distortionless translation of signal components within a desired range of frequencies, the effective inductance must :be approximately constant and the phase-shift factor must have a substantially linear relationship with frequency. Hence, it becomes apparent that the interturn inductive coupling which introduces a variation in the effective inductance with frequency deteriorates the phase-shift characteristic and introduces distortion into the network.

Coming now toa consideration'of theefiect of the core construction, it is seen that the portions of the network associated with the system of conductive surfaces Ila-l Id exhibit the same values of distributed series inductance and distributed shunt capacitance. The intermediate portions of the network, associated with the system of conductive surfaces comprising conductive rings lla-| Ie' may have approximately the same distributed capacitance per unit length, but exhibit a reduced effective inductance because of the low resistivity to circulating currents of the conductive rings. These rings further tend to decouple the network sections interposed between succeeding ones of the rings. Essentially, therefore, the described core structure causes variations of effective inductance along the network and, in particular, its ring segments lIa'-ll e, inclusive, periodically decrease the effective inductance so that alternate portions of the network have substantially different values of series inductance and shunt capacitance.

In the arrangements illustrated in copending application Serial No. 626,357 referred to above, a similar result is obtained by periodic variations of the distributed shunt capacitance along the network and it is shown that this variation of capacitance simulates a low-pass filter network in the time-delay arrangement. By way of a similar analysis it may be demonstrated that in the present invention, wherein there is a periodic variation of inductance, a low-pass filter is also simulated in the time-delay network. A low-pass filter tends tocause asymmetrical distortion of an applied symmetrical pulse in a sense which is complementary to the asymmetrica1 distortion attributable to the interturn inductive coupling of winding Ill. The spacing and width of the conductive rings Halle' which introduce and determine the characteristics of the low-pass filter are proportioned relative to the interturn inductive coupling of winding It so that an applied symmetrical pulse is translated through the network with a distortion that is less than the larger of the asymmetrical distortions caused by the winding and the simulated low-pass filter. In some useful applications of the invention satisfactory phase characteristics are obtained by arranging conductive member ll so that its conductive rings have a spacing at least equal to the diameter of winding ID. The precise proportioning of the rings may be determined as follows.

The phase-shift frequency characteristic of a conventional low-pass filter is represented by the curve of Fig. 2a, where 'fc is the cutofi frequency of the filter. The corresponding characteristic of a time-delay network including -a distributed winding having a substantial inductive coupling between turns but having no phaseshift compensation is illustrated by full-line Curve A of Fig. 2b. Assuming the network is to translate signal components over the frequency range designated OfL, the desired phase-shift characteristic for distortionless translation is shown by the dash-dot Curve B. From a comparison of Curves A and B it is clear that the uncompensated network produces an undesired distortion of signal components within the intended operating frequency range. Where too little compensation is provided by the simulated low-pass filter, the composite phase-shift characteristic of the network may be in accordance with Curve D. For this condition an undesired phase distortion is encountered. On the other hand,too much compensation i'nodifies' the phase-shift characteristic of the network as shown by Curve E, which is likewise undesirable since it distorts, in an opposite sense, signal components within the required range OfL. Curve F is the composite characteristic for optimum compensation over the desired range.

In discussing the characteristics of Fig. 2b, conditions of undercompensation and overcompensation have been mentioned. In practical constructions of the embodiment of Fig. l, the extent of compensation varies with the spacing and width of the conductive rings lla-l le. Where the spacing and width of the rings are too small, the condition of Curve E prevails while the phase characteristic of Curve D results from a width and spacing of the rings which are too large. The optimum condition is intermediate these extremes and is determined in any case with reference to the degree of interturn inductive coupling of winding l0 and the desired operating frequency range of the network. A generally useful spacing of the rings is such that the delay of the winding between succeeding rings is equal to one-half the period at the cutoff frequency fr. of the simulated low-pass filter.

A time-delay network having a construction of Fig. 1 and compensated to exhibit the phaseshift characteristic represented by Curve F of Fig. 2b, translates an applied symmetrical pulse substantially free of the asymmetrical distortions attributable to the interturn inductive coupling of winding 10 and the simulated low-pass filter of the network. This is true even though the applied pulse may have a duration less than the delay of the network.

It may be convenient to view the character-- istics of the described network with reference to its effective inductance. The reduction of effective inductance with frequency in the ordinary, uncompensated network including a winding which has a substantial interturn inductive coupling is indicated by Curve A of Fig. 3. The effective inductance of a lumped time-delay transmission line with uncoupled sections, an effect introduced by the conductive rings Ha- I le', is represented by Curve C. Curve B shows the resulting variation of effective inductance. reflecting the conjoint influence of the inductance characteristics A and C. The compensated or phase corrected network exhibits a substantially uniform effective inductance over the frequency range O-fL.

The modification of Fig. 4 is similar to that of Fig. 1 and corresponding components thereof are designated by the same reference characters. In this case, however, the winding is wound over a solid core IQ of insulating material and the con-- ductive member I l is a capacitive shield in the form of a woven metallic braid surrounding the Winding and insulated therefrom by the dielectric sleeve [2. It is here contemplated that the conductive member I I be uniform throughout its length although it may be analyzed as the equivalent of the system of conductive surfaces Ila-l Id of Fig. 1. In this embodiment, the conductive rings |la'-He are disposed about the external periphery of the winding and the metallic braid. With this construction the rings may very conveniently be made of a low resistive material, such as copper, and may be fastened into the assembly by a crimping process. The ring spacing is preferably approximately equal to the ring diameter.

The. modification of; Fig. 5. is; generally similar to that of Fig. 1, having a conductive core ll coaxiallydisposed within Winding it. The core-may have any well-known. construction and may; for example, be a conductive cylinder having one or more longitudinal slots. extending along most of its length for reducing eddy current losses... The conductive rings I la-He' are. spaced along; the outer periphery of the winding and may be separated by and integrated with a conductive shield [9 which, preferably, is slotted intermediate the rings.

Where the conductive rings are not integrated with the conductive member used for establishing the predominant component of distributed shunt capacitance in the network, one may be. positioned within the coil andthe. other may be external thereto. In the embodiment of Fig.5. there is: illustrated an arrangement in which the conductive member is used as a core while the conductiverings are spaced along the outer periphery ofthe winding. The reverse relationship isshown in Fig. 6: where the winding is supported upon a dielectric material or insulated core H3 in the form of a cylinder. he distributed shunt: ca pacitance of the network is established. by the capacitive coupling between the windin and the conductive member H which, in this case, may bea woven metallic braid. The conductive rings l'I'a'-I-l'e are coaxially aligned Within sleeve t8".

Each of the described embodiments of the invention has: the advantage of minimum phase distortion over a selected operating frequency range. This desiredresult flows from the phasecompensating efiect of the simulated low-pass filter resulting from the use of the spaoedi con.- ductive rings. The arrangement has a simplified construction and may exhibit a long time delay while, at the same time, having a small physical size.

The networks illustrated may be coupled through their terminals into any desired signaltranslating system. They are subject to a Wide variety of applications and may be utilized, for example, to obtain a desired time delay of applied transient signals. Also, through appropriate termination of the output terminals, echoes or reflections of an applied signal may be produced as with well-known reflecting transmission-line arrangements.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will beobvious tothose skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What isclaimed is: 1-. A time-delay network adapted to translate a signal pulse the duration of which maybe less than the delay of the network comprising: an

elongated winding having a substantial inductive coupling between turns tending to cause u asymmetrical distortion in one sense of an applied symmetrical pulse; one system of conductive surfaces associated in coaxial relation with said winding, having a high resistivity to circu-. lating currents, and. insulated from but electrically coupled to a major portion of. said winding to provide a. distributed shunt capacitance for said network; and. another system of conductive surfaces comprisin a plurality of rings having a.

low resistivity to circulating currents and spaced along said. winding periodically to vary the-iii ductance thereoi to simulate in said network a low-pass filter'tending to cause asymmetricaldise tortion in a complementary sense of an applied symmetrical pulse, the spacing: and width of said rings; being proportioned relative to the interturn inductive coupling, of said winding so that an ap: plied symmetrical pulse is translated through said network with a distortion substantially less than the larger of'said asymmetrical distortions caused by said. winding and said simulated low-pass filter.

2. A time-delay network adapted totranslate a signal pulse the duration of which may be less than the delay of the. network comprising: an elongated winding having a substantial inductive coupling between turns tending tov cause asymmetrical distortion in one. sense of an applied symmetrical pulse; an. elongated conductive member associated in coaxial relation with said winding, having a high resistivity to circulating currents, andinsulated' from but electrically coupled to a major portion of said Winding to providea distributed shunt capacitance for said network;

and a plurality of rings having a low resistivity to circulating currents and spaced along said winding periodically to vary the inductance thereof to simulate in said network a low-pass filter tending to cause asymmetrical distortion in a complementary sense of an applied symmetrical pulse, the spacing and width of said rings being proportioned relative to the interturn inductive coupling of said winding so that an applied symmetricalpulse is translated through said network with a distortion substantially less than the larger of said symmetrical distortions caused by said winding and said simulated lowpass filter.

3. A time-delay network adapted to translate a signal pulse the duration of which may be less than the delay of the network comprising: an elongated winding having a substantial inductive coupling between turns tending to cause asymmetrical distortion in one sense of an applied symmetrical pulse;- an elongated conductive core member coaxially disposed within said winding; having a high resistivity to circulating currents, and insulated from but electrically coupled to a major portion of saidwinding to provide a distributed shunt capacitance for said? networkqxand a; plurality-ofrings having a low resitivity to circulating currents and spaced along theouter periphery of said winding periodically to vary the inductance thereof to simulate in said network a low passfilter'tendingz to cause asymmetical distortion. in. a complementary sense of an applied symmetrical pu1se, the Spacing and width of. said rings being proportioned relative to; the interturn inductive coupling of saidwinding so; that an applied symmetrical pulse is translated.

through said network with. av distortion substantially lessthan: the larger of said symmetrical distortions caused by said winding and said simulatedlow-pass filter.

4. Atime-delay network. adaptedto translates. signal pulsethe duration of which may be less than the delay of. the network comprising: an elongated winding having a substantial inductive coupling between turns tending to cause asymmetrical. d'mtortion in one sense of. an applied symmetrical pulse; an elongated conductive member associated. coaxial relation with said winding, having a, high resistivity to circulating currents, and insulatedfrom but electrically GQLlr pled to a major portion. of said, winding to pro;- videa distributedshunt capacitance. for said net:-

Work; and a plurality of rings having a low resistivity to circulating currents and spaced along the outer periphery of said winding periodically to vary the inductance thereof to simulate in said network a low-pass filter tending to cause asymmetrical distortion in a complementary sense of an applied symmetrical pulse, the spacing and width of said rings being proportioned relative to the interturn inductive coupling of said Winding so that an applied symmetrical pulse is translated through said network with a distortion substantially less than the larger of said symmetrical distortions caused by said winding and said simulated low-pass filter.

5. A time-delay network adapted to translate a signal pulse the duration of which may be less than the delay of the network comprising: an elongated winding having a substantial inductive coupling between turns tending to cause asymmetrical distortion in one sense of an applied symmetrical pulse; an elongated conductive member associated in coaxial relation with said winding, having a high resistivity to circulating currents, and insulated from but electrically coupled to a major portion of said winding to provide a distributed shunt capacitance for said network; and a plurality of rings having a low resistivity to circulating currents and spaced along the inner periphery of said winding periodically to vary the inductance thereof to simulate in said network a low-pass filter tending to cause asymmetrical distortion in a complemetary sense of an applied symmetrical pulse, the spacing and width of said rings being proportioned relative to the interturn inductive coupling of said winding so that an applied symmetrical pulse is translated through said network with a distortion substantially less than the larger of said symmetrical distortions caused by said winding and said simulated low-pass filter.

6. A time-delay network adapted to translate a signal pulse the duration of which may be less than the delay of the network comprising: an elongated winding having a substantial inductive coupling between turns tending to cause asymmetrical distortion in one sense of an applied symmetrical pulse; one system of conductive surfaces associated in coaxial relation with said winding, having a high resistivity to circulating currents, and insulated from but electrically coupled to a major portion of said Winding to provide a distributed shunt capacitance for said network; and another system of conductive surfaces comprising a plurality of rings having a low resistivity to circulating currents and spaced along said winding periodically to vary the inductance thereof to simulate in said network a low-pass filter tending to cause asymmetrical distortion in a complementary sense of an applied symmetrical pulse, said rings having a spacing at least equal to the diameter of said winding and a width proportioned relative to the interturn inductive coupling of said Winding so that an applied symmetrical pulse is translated through said network with a distortion substantially less than the larger of said asymmetrical distortions caused by said winding and said simulated low-pass filter.

7. A time-delay network adapted to translate a signal pulse the duration of which may be less than the delay of the network comprising: an elongated winding having a susbtantial inductive coupling between turns tending to cause asymmetrical distortion in one sense of an applied symmetrical pulse; one system of conductive surfaces associated in coaxial relation with said winding, having a high resistivity to circulating currents, and insulated from but electrically coupled to a major portion of said winding to provide a distributed shunt capacitance for said network; and another system of conductive surfaces comprising a plurality of rings having a low resistivity to circulating currents and spaced along said winding periodically to vary the inductance thereof to simulate in said network a low-pass filter tending to cause asymmetrical distortion in a complementary sense of an applied symmetrical pulse, the spacing and width of said rings being proportioned relative to the interturn inductive coupling of said winding so that an applied symmetrical pulse is translated through said network substantially free of said asymmetrical distortions caused by said winding and said simulated low-pass filter.

MICHAEL J. DI TORO.

REFERENCES CITED UNITED STATES PATENTS Name Date Roosenstein Oct. '7, 1941 Number 

